Guided missiles and projectiles have need for a compact short life source of pressurized gas on board to aid guidance systems and cool infrared detectors during inflight. A small pressure vessel hermetically sealed according to the invention retains a highly pressurized gas for this function. In flight, once the pressurized gas is selectively released from its container, it flows through a system to provide energy for uncaging gyroscopes, cooling infrared detectors, and maneuvering control surfaces.
One of the problems encountered with the use of the small highly pressurized vessels is that no method has been developed for effectively sealing in the pressurized gases to provide it with a long shelf life whereby the missile or projectile in which it is used can be stored for an extended time and have high reliability when called upon.
Sealing of highly pressurized vessels is the subject of many patents, but none provide high reliability over an extended period and many of the arrangements for accomplishing the task are complicated and awkward to perform. Some arrangements call for a bottle to be filled inside a larger pressurized vessel. See, for example, U.S. Pat. No. 3,577,696 where highly pressurized gas is introduced into the bottle by leaking it past loosely engaged cap threads, and after pressurization, the cap is tightened to compress a seal element to prevent leakage. This arrangement defines nothing more than a gasket which, in time, for many reasons, allows leakage of pressurized gas, and is, therefore, not reliable. This is not an acceptable method for use on the container disclosed herein because its thin fragile reduced neck portion will not withstand the high torque necessary to compress a gasket.
Compressed or soldered pigtails have long been used for sealing a fill neck of a container, but this involves difficult working arrangements at elevated pressures and, furthermore, the final seal is unreliable.
A tool for filling and sealing a pressurized vessel is disclosed in U.S. Pat. No. 3,844,089. It teaches the sealing of a fill opening by wedging a plug radially outwardly into contact with passage walls. Neither does this disclosure provide an effective and reliable seal for extremely high pressures over an extended life.
U.S. Pat. No. 3,952,395 teaches the method of plugging and sealing a hole in a ductile material by press fitting therein a spherical ball of the same type material. This method cannot be applied to the pressurized vessel disclosed herein because it cannot be of a ductile material due to the very high pressurized gases which it must contain.
One method of sealing a pressure vessel identical to the one disclosed herein for confining highly pressurized gas is disclosed in U.S. Pat. No. 4,255,916 assigned to the United States, as represented by the Secretary of the Navy, and upon which the present invention is an improvement. While its structure and operation is fully described in the patent, brief reference will be be made thereto. Solder joint 25 in that patent is first established between the bottom of valve body 16 and mounting flange 15. Then, a source of highly pressurized gas is coupled to inlet 20 of valve body 16 and allowed to flow past ball 18 and on through the passage to chamber 11. When the desired pressure is reached within chamber 11, the charging line is removed from inlet port 20 and pressure acting against plastic ball 18 from inside the chamber seats it against valve seat 24 to define only a temporary seal. Immediately thereafter, inlet port 20 is closed by applying solder 26. The problem with the arrangement and method taught in U.S. Pat. No. 4,255,916 is that each solder joint is under a constant high pressure and will eventually leak. As mentioned, seated ball 18 provides only a temporary seal until solder joint 26 is established. The fact is that the temporary seal allows continuous leaking of a small amount of the highly pressurized gas even while solder 26 is being applied and while setting. This interferes with hermetic integrity of the joint. It has become known to applicants by microscopic examination of solder joint 26 that gas leaking past the temporary seal of ball 18 forms small passages through and around the solder before setting has occurred. These passages permit continued minute leakage of the pressurized gas which eventually allows its complete dispersion from changer 16.
The improved sealing arrangement herein is directed toward overcoming the identified shortcomings in the prior art and especially those in U.S. Pat. No. 4,255,916.